1. Field of the Invention
The present invention relates to liquid-crystal display devices in which pixel electrodes are formed, such as thin-film-transistor liquid-crystal display devices and passive-matrix liquid-crystal display devices, and in particular, to a liquid-crystal display device formed by techniques for causing pixel electrodes to generate lines of electric force, which is effective in driving the liquid crystal, and for reducing the number of masks used to form layers.
2. Description of the Related Art
FIG. 6 shows an example of the structure of a general liquid-crystal display device. The liquid-crystal display device A of this type has a pair of opposed substrates 1 and 2, liquid crystal 3 provided therebetween, and polarizers 4 and 5 disposed on the external surfaces of the substrates 1 and 2. When the liquid-crystal display device A is a thin-film-transistor type, on the substrate 1 there are arranged source interconnections and gate interconnections in the form of a matrix, and there are provided thin film transistors as switching devices and pixel electrodes on regions at which the source interconnections and the gate interconnections intersect. On the other substrate 2 is formed a common electrode. By supplying a potential difference between the pixel electrodes on the regions and the common electrode opposed thereto so as to apply a desired electric field to the liquid crystal provided between both electrodes, the alignment of the liquid crystal can be controlled.
Also, when the liquid-crystal display device A is a passive matrix type, strip electrodes are formed on the substrates 1 and 2 so as to be in the form of a matrix. By applying an electric field to the liquid crystal in regions where the upper and lower electrodes intersect, the alignment of the liquid crystal can be controlled.
In addition, according to the liquid-crystal display device A, in order to efficiently apply an electric field to the liquid crystal provided between the substrates 1 and 2 it is important to arrange the pattern of lines of electric force generated between the pixel electrodes on the substrate 1 and the common electrode on the substrate 2 having the liquid crystal therebetween.
Accordingly, as shown in FIG. 7, there is shown a conventional liquid-crystal display device B including each pixel electrode 7 formed on a substrate 6 and counter electrodes 9 formed on another substrate 8, in which the counter electrodes 9 are formed by bisection by a slit 10 formed to be opposed to the center of the pixel electrode 7, and a peripheral electrode 12, peripheral to the pixel electrode 7, is embedded in an insulating film 11, with the counter electrodes 9 and the peripheral electrode 12 being grounded.
In the liquid-crystal display device B having the structure shown in FIG. 7, a pattern of lines of electric force is regularly generated from the middle of the pixel electrode 7 to the slit 10 between the counter electrodes 9, and the pattern of lines of electric force, peripheral to the pixel electrode 7, is curved downward as shown in FIG. 7. Thus, the pattern of lines of electric force in the middle of the pixel electrode is uniform, and the pattern of lines of electric force, peripheral to the pixel electrodes, is distorted, so that the alignment direction of the liquid crystal changes along the lines of electric force, and the viewing-angle range of the liquid-crystal display device advantageously expands. However, the liquid-crystal display device B has the following defects.
According to the structure shown in FIG. 7, it is required that the position of the slit 10 be opposed to the center of the pixel electrode 7 and the positions of ends of the counter electrodes 9 be adjusted to the periphery of the pixel electrode 7. However, even if the present substrate alignment technique is used, it is difficult to reduce an error in the alignment of the substrates 6 and 8. If the position of the slit 10 is off the center of the pixel electrode 7, and the positions of the peripheries of the counter electrodes 9 are off the periphery of the pixel electrodes 7, the above requirement cannot be satisfied, which causes a possibility of destroying the pattern of lines of electric force.
By comparing the liquid-crystal display device B with a conventional liquid-crystal display device having a general structure using a continuous electrode without the slit 10 as a counter electrode, it is found that the counter electrode 9 needs to be patterned and an additional one mask is necessary when using a lithographic technique to form the counter electrode 9. Accordingly, the production process is complicated, which disadvantageously reduces the yield.